Apex domains cannot have CNAME records.
Question and response
Question
dig IIJ.NET. NS
Answer
iij.net. 4 NS dns0.iij.ad.jp.
iij.net. 4 NS dns1.iij.ad.jp.
Authority
The response has no authority records.
Additional
dns0.iij.ad.jp. 4 A 210.130.0.5
dns1.iij.ad.jp. 4 A 210.130.1.5
dns0.iij.ad.jp. 4 AAAA 2001:240:0:0:0:0:0:105
dns1.iij.ad.jp. 4 AAAA 2001:240:0:0:0:0:0:115
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0